1. Field of the Invention
The present invention relates to a hybrid industrial vehicle including an engine and an electric motor as its drive source.
2. Description of the Related Art
Hybrid industrial vehicles each include an engine and an electric motor as its drive source, and are therefore capable of outputting a large amount of power while being excellent in energy efficiency. Hybrid forklifts have been known as an example of such hybrid industrial vehicles.
Since requiring large drive power for steering operation, many forklifts employ full hydraulic power steering in which the steering wheel and the road wheels are connected purely hydraulically, instead of a power steering as in the cases of passenger vehicles in which the steering wheel and the road wheels are connected by mechanical shafts and gears and steering is assisted by an actuator. Most of forklifts with the full hydraulic power steering are configured such that pressure oil for the drive for steering is supplied from a hydraulic pump which is also used to supply pressure oil for the drive for cargo handling.
Patent Document 1 listed below discloses a hybrid forklift having such configuration. The configuration of this hybrid forklift will be described based on FIG. 15. FIG. 15 is a configuration diagram of a drive system of the conventional hybrid forklift.
As shown in FIG. 15, the conventional hybrid forklift includes an engine 1, a battery 2, a first electric motor 3, a second electric motor 4, a first hydraulic pump 12, a second hydraulic pump 13, a first gear train 9, a second gear train 5, and so forth.
An output shaft 1a of the engine 1 is connected to the first gear train 9 through a one-way clutch 15 transmitting power only in a direction from the engine 1 side to the second gear train side, the second gear train 5, a torque converter 6, a transmission 7, and a forward-reverse clutch 8 provided to the transmission 7. Meanwhile, an output shaft 3a of the first electric motor 3 is connected directly to the first gear train 9. The first gear train 9 is connected to front wheels (drive wheels) 11 through a front axle 10 including a differential gear (not illustrated) and the like.
This hybrid forklift therefore runs when power of the first electric motor 3 and power of the engine 1 are transmitted to the front wheels 11 through the first gear train 9 to rotationally drive the front wheels 11. Note that the first electric motor 3 is actuated when supplied with electric power from the battery 2 through a first inverter 14.
Meanwhile, the second electric motor 4 has its output shaft 4a connected to the first hydraulic pump 12 through the second gear train 5. The second electric motor 4 is actuated when supplied with electric power from the battery 2 through a second inverter 17. The output shaft 1a of the engine 1 is also connected to the first hydraulic pump 12 through the second gear train 5. Thus, power of the engine 1 and power of the second electric motor 4 are transmitted to the first hydraulic pump 12 through the second gear train 5 to thereby rotationally drive the first hydraulic pump 12. As a result, pressure oil discharged from the first hydraulic pump 12 is supplied to a hydraulic cylinder in a cargo-handling hydraulic system and a hydraulic cylinder in a steering hydraulic system, which are not illustrated.
The input side of the second hydraulic pump 13 is connected to the hydraulic cylinder in the cargo-handling hydraulic system, whereas the output side thereof is connected to the second electric motor 4 through a one-way clutch 16 and the second gear train 5. Thus, while the lift is being lowered, the pressure oil discharged from the hydraulic cylinder in the cargo-handling hydraulic system rotationally drives the second hydraulic pump 13. By this second hydraulic pump 13, the second electric motor 4 is rotationally driven to function as a generator. The electric power generated by the second electric motor 4 functioning as a generator is charged into the battery 2 through the inverter 14 (i.e., cargo-handling regeneration is performed). Note that the engine 1 is started by an unillustrated starter motor dedicated to starting the engine.    Patent Document 1: Japanese Patent Application Publication No. 2008-7089    Patent Document 2: Japanese Patent Application Publication No. 2006-273514